Automating candidate selection for CT drilling.pdf

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Copyright 2001, Society of Petroleum Engineers Inc.

This paper was prepared for presentation at the SPE/ICoTA Coiled Tubing Roundtable held inHouston, Texas, 78 March 2001.

This paper was selected for presentation by an SPE Program Committee following review ofinformation contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not been reviewed by the Society of Petroleum Engineers and are subject tocorrection by the author(s). The material, as presented, does not necessarily reflect anyposition of the Society of Petroleum Engineers, its officers, or members. Papers presented atSPE meetings are subject to publication review by Editorial Committees of the Society ofPetroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper

for commercial purposes without the written consent of the Society of Petroleum Engineers is

prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300words; illustrations may not be copied. The abstract must contain conspicuous

acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O.Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

Abstract

As fields are becoming more mature and improved reservoirinterpretation is identifying so-called By-passed hydrocarbons, moresidetracks will be required. Selecting a well to reach a certain target inthe reservoir can be a long task as a number of issues have to beconsidered. Using an auditable process for selecting the optimumsidetrack method and the best wellpath to reach a certain target cantake a drilling engineer several months on a multi well development. Inorder to optimise this process all of the relevant parameters have to beconsidered. An automated system using a database now allows quick

identification of the correct sidetrack method and selects the mostsuitable wellpath for the sidetrack. This fully transparant method startswith the reservoir target and then works through all the issuesassociated with the well selection process.

This paper describes the Candidate Selection Methodology, examplesof the criteria utilised to evaluate the suitability of the Drilling Techniqueand examples of the speed of Selection for a candidate Well and theoutput of the process.

Background

As the North Sea Fields mature pockets of oil are becoming isolatedand are decreasing in size. Because of this conventional methods arereaching their economic threshold. Increasingly operators are looking

to alternative methods to exploit this stranded oil. Techniques such asCoiled-Tubing Drilling, Through Tubing Rotary Drilling, HydraulicWorkover Drilling as well as conventional drilling are being considered.The competent selection of the best method or combination of thesemethods from an operational, drillability and commercial perspective isnow a necessity. In a multiwell field development where often 40 ormore wells are drilled, selecting the best sidetrack candidate is acomplicated task. Wells have to analysed on their function i.e. injectioror if producer then the relative worth and water cut should beconsidered. The well then has to be able to reach the selectedreservoir target and then the mechanical aspects of the well have to bereviewed based on the drilling method selected.

In order to facilitate this whole process a software system wasdeveloped which now allows a geologist or a reservoir engineer toselect a target and provide the drilling engineer with a suitable targetwell. This elliminates a significant amount of time in the well planningprocess and allows infill wells to be planned better and faster.

Development

When initially designing the operation of the Well Analysis andSelection Process (WASP), the goal was to design a structuredapproach to planning Specialist Drilling Techniques and choosing thebest candidate wellpath in order to achieve a successful operation.There was little experience throughout the North Sea with regard tothese operations so it was essential that sidetracks planned usingthese techniques did not overlook crucial information. By automatingthe whole process, the Candidate Well selection can be mapped out.

During the first stages of development, the tool was a spreadsheetlisting the important information that could effect the success of theoperation. Each element was given a complexity score dependent onthe results obtained. The criterion was separated into two mainsections one dependant on the condition of the existing well and theother, dependent on the engineering requirements for the proposedsidetrack. By mapping out each step taken, finding the bestcandidate/target option became faster and the process wastransparent. If any of the information changed regarding the wells or aproposed sidetrack, then it was easy to go back and retrace thesteps taken.

The Well Analysis and Selection Process (WASP) is now a fullyautomated system using an Access Database and visualbasic scripting.

Well Analysis and Selection Process

The Well Analysis and Selection Process (WASP) program (fig.1) wasdesigned to provide a systematic and efficient technique of selectingpossible candidate wells for Through-tubing Sidetracks using SpecialistDrilling Techniques. The program compares various techniques suchas Coiled-Tubing Drilling, Through-tubing rotary Drilling, HydraulicWorkover Unit Drilling as well as conventional Drilling Methods. The

WASP program applies a systematic approach to select the bestpossible candidates within a well portfolio for a specified target. Thecandidate wells are then ranked by complexity. By automating theprocess the time taken to select these wells is significantly reducedand unsuitable candidates are rejected automatically in the earlystages of the process. The WASP program runs in four stages:

Find Wells within a given distance from a reservoir target.

Operability assess the complexity of access through existingcompletion and kicking-off from a selected point in the well.

Drillability assess the complexity of drilling from the kick-off pointto the specified target using a specific drilling technique.

Results a ranked comparison of the overall Operability andDrillability results.

SPE 68438

Automating Candidate Selection for Coiled-Tubing DrillingM. Brown, S. Nas and I. Lusted, Leading Edge Advantage Ltd.


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2 M. BROWN, S. NAS AND I. LUSTED, LEADING EDGE ADVANTAGE LTD. SPE 68438

The Wells Database

For the first two stages of the WASP program analysis to run, a certainamount of Well Information is required. In order to maintain as muchautomation as possible, an electronic wells database was created tostore the critical information (fig. 2). The program could then query thisdatabase for the data it required. This database was expanded toinclude general Well information that would also be contained within a

Well file. This allowed the user of the system to view data anddiagrams of a specific well quickly without searching through reams ofpaper files. It was quickly realised that by creating an electronic Wellsdatabase, the analysis time was greatly reduced. The Wells Databasecurrently used by the WASP program allows the following informationto be stored:

Well OverviewThis contains General information regarding the Well, i.e:- Well Name and Licence Name- Field and Platform well refers to.- Type of Well and Completion Age.- Slot Location.- TD and KOP.- Maximum Deviation and Dogleg.- Well Cleaniless (Scale etc.)- Crane Capacity.

- MAASP- Estimated Bottom Hole Temperature.- Tubing Leak.

Casing and Liner informationThis section of the database contains:- Details of Casings used (Size, Grade, Coupling etc.).- IDs of Casings.- Casing Shoe Depths- Details of Liners used (Size, Grade, Coupling etc.).- IDs of Liners- Liner Shoe Depths.- Tops of Cement.

Completion- Tailpipe Depth

- Completion IDs- Packers.- Chrome or Plastic Coated Tubulars

Previous Operations- An operations history

Surface Equipment- Description of Christmas Tree- Details of Compact Spool- Gasket Sizes etc.

Perforations- Current and Isolated Perforations- Depths- Guns Used

- Date Perforated.

Deviation- Well trajectory imported from existing Spreadsheet orentered manually.

Fluids and Formation- Muds used for Sections drilled.- LOT information- Lithology information.

Highlights/Lowlights- Details of particluar Operations to be entered so knowledgeis not lost.

The database can be linked to existing databases in order to capturethe relevant information. However, lots of well files are still paper basedor are on incompatible electronic formats. If this is the case, data willinitially have to be entered manually. This data input task can still betime-consuming, but it does not require a highly qualified drillingengineer to carry out these tasks. Once the information is stored, it canbe quickly and easily searched and the database can further be usedfor other analysis, such as reviewing installed well equipment in a field.

Wells within Distance

In order for the first stage of the analysis to take place, a target mustbe selected. The target information is stored as the initial step of theWASP program (fig.3). The Geological co-ordinates and TVD of thetarget is required as well as a general description. The depth can beentered as below drill floor or a mean sea level. If below drill floor isselected then the drillfloor elevation must be entered. The targetestimated reserves are entered for information, as this is the main goalof the operation. It is the intention that future systems will calculate aninitial cost estimate and provide economics of a sidetrack as part of thesystem output.

Once a target has been selected the user can then specify a distance

around the target and a minimum depth that is considered to kick-offfrom. This program takes the deviation survey data stored in thedatabase and the slot co-ordinates from the Well Overview section ofthe database in order to calculate whether the deviation points fall withthe select area around the target (fig.4). If they do not fall within therange then the well is discounted immediately.

At this stage in the program, certain wells can be discountedautomatically by the rejection process. For a given type of completionthe maximum age and minimum ID can be specified. Those wellsnominated as good producers can also be discounted. The Wells thatmeet the specified criteria are listed by TVD from Target. However,the information may be listed by Well Name, Completion Type orDistance from Target. More than one point for the same well may belisted, as the program will show all deviation points that match thespecified criteria. This allows several positions in the well to beselected as viable to go through to the next stage of the SelectionProcess. Only wells selected as viable may be analysedfor Operability.

Operability

Once several candidates have been selected, an analysis of the easeof access through the existing completion and general impact to theplatform can be performed. An Operability Mask (fig.5) was created tosearch out certain information from the Wells Database and give ascore to each element of the Mask dependant on the complexity.

The Completion is analysed for minimum IDs, any chrome tubulars,plastic coated tubulars. The kick-off depth is assessed, by looking atwhere the tailpipe, production packers and casing shoe depths are inrelation to it.

The Operability Mask looks to see if there are any perforations abovethe kick-off point. Assessment of the well cleanliness, CITHP, tubingleaks and reservoir temperature takes place.

At this stage, an initial assessment of the interface with the platformcan be done, by choosing a possible technique (for example, CTDconcurrent will have a different effect to the platform than CTDstandalone operations). This does not tie the user to this techniquewhen moving to the Drillability Analysis.

The mask looks for the crane capacity of the platform, as this can be abig factor when lifting equipment for operations such as coiled-tubingdrilling. Each of these elements is looked for within the database, and


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SPE 68438 AUTOMATING CANDIDATE SELECTION FOR COILED-TUBING DRILLING 3

dependant on the findings, is given a complexity score stated bythe mask.

A Master Operability Mask is contained within the WASP program andcan be accessed through the Main Menu. This allows the user, ifrequired, to change certain complexity scorings. Certain Operatorsmay have different experiences with different techniques in localenvironments, so the ability for the Mask to be flexible was important.

Once the analysis has taken place, the Operability Scores are listed(fig.6). It is possible to save these results and leave the program at thispoint. This allows the drilling engineers to look at the best candidatesfrom this stage in more detail in order to move on to theDrillability Analyser.

Program Scoring

WASP uses two scoring mechanisms. A number complexity score anda traffic light system to highlight which number scores are suitable. Asmentioned earlier the masks scores the relative elements of the maskfrom 1 5 (5 highest complexity). However, a score of 5 for any oneelement in the mask can be a serious set back in itself. Therefore, theprogram will weight a high score more so than a low score in anexponential manner i.e.

n

Where:Complexity

Score n

Program

Score n

1 1 1.00

2 0.8 1.74

3 1 3.00

4 1.2 5.28

5 1.5 11.18

The mean of the program scores will be taken as the score for thatparticular option.

The traffic light system is used to judge which scores are deemedacceptable (fig.7). This allows Management to judge the risk ofcarrying out particular operations.

WASP is set up initially as follows:< 2.5 = green = acceptable2.53.5 = amber = possibly acceptable> 3.5 = red = unacceptable

Any User can alter this traffic light set-up with Administration access, ifrequired. Again allowing the program to be f lexible.

Wellpath Options

Before the Drillability Analysis can be carried out the Drilling Engineerwill still have to develop potential wellpaths in the normal manner.

Using the candidate wells chosen from the Operability stage, at leastone wellpath option must be designed for each candidate. There canbe more than one wellpath option for each well using the same or adifferent drilling technique. For each wellpath option the drillingengineer will still have to design a well trajectory, carry out torque anddrag analysis, hydraulic calculations and other well design issues usingthe usual well planning tools. The software has deliberately notintegrated trajectory planning, torque and drag and hydraulics asdifferent operators have different methods, procedures and systems todesign the optimum trajectory and drilling systems.

Once the drilling engineering information has been gathered, thewellpath options can be created for the candidate Wells (fig.8). Whencreating a wellpath option the drilling technique will need to bespecified. The WASP program automatically requests therelevant information.

Once all the questions are answered, the information given by thedrilling engineer can be analysed using the Drillability Masks. As therecan be more than one wellpath for each candidate well, the program

has the ability to compare different techniques for the same candidatewell against another candidate well with various wellpaths usingdifferent drilling techniques. The wellpath option can be saved andedited at any time using the edit wellpath option, which can beaccessed at this stage or from the main menu (fig.9).

Drillability

Once the Wellpath Options are entered, the Drillability Score iscalculated using the Drillability Mask (fig.10) specific to the DrillingTechnique specified. There are four Master Drillability Masks.

Coiled-Tubing Drilling

Through-Tubing Rotary Drilling

Hydraulic Workover Unit Drilling

Conventional Drilling.

When the drilling method is selected, the program automatically selectsthe Drilling Mask relevant to the chosen technique in order to score theDrillability. The Mask compares the information provided by the drillingengineer with the relevant mask and assigns a Complexity score. Therelevant drilling mask checks a number of parameters such as:1. Open hole length.2. Maximum Dogleg and Collision index of the Well trajectory.3. Annular Velocities in the open hole.4. Annular Velocities in Tubing and at the 45-60 deg angle section

(if applicable).5. The Fracture gradient versus the ECD value.6. Overbalance Pressure.7. Pump Pressure8. The expected Maximum WOB and Maximum Effective Pull at TD.

There are also a number of subjective entries that the engineerhas to input. The higher the score entered for these entries, thehigher the risk. These are:

9. Estimate of days in order to prepare the well for sidetracking.10. Any anticipated formation problems.11. Completion complexity12. Learning Curve.This allows a higher score for an Operator with

little experience using such techniques but the score will godown as experience grows.

13. Another important issue for Through-tubing sidetracks is theretention of the production from the main bore. Therefore ascore, dependant on the Junction Complexity of the sidetrackis calculated.

Once each Wellpath Option has been scored using the correct Mask,the results can then be moved through to the f inal results page.

As with the Operability Masks, new Drillability Masks can be createdbased on the Master Masks for each drilling technique dependant onthe users experience. Certain elements in the mask may be more ofan issue for some Operators than with others (i.e. Formation Problems)and therefore, the scoring or weighting values can be altered toreflect this.

Final Results

The final results page is used as a comparison tool so that the bestCandidate Well/Well Path Option can chosen for the specific Target.The Scores for Drillability are listed beside the scores for Operability.Both scores are added together and colour coded dependant on thehighest colour rating of the two. The candidate Well is listed beside the


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Wellpath Option Name and the Drilling Technique and the kick-offdepth selected. The Target Name and details are listed against thename of the User. This allows the whole process to be traceable. Theresults are ranked in order of the Final combined score so it is clearwhat the best candidate for the sidetrack will be (fig.11).

Advantages

The main advantages for the automating of candidate selection forspecialist drilling techniques have already been proven through use.From a database of almost 200 wells, the first stage of the analysis tofind the wells within a specified distance of the target, although this isgenerally the longest calculation the program executes, it only takes 2to 3 minutes. Significant time savings are made when comparing themanual selection process of searching for wells on spider plots.

Good Producers, old completions or narrow completion restrictions canbe eliminated at the beginning of the candidate process.

The Operability analysis of the selection process takes seconds tocalculate. This allows the Drilling Engineer or Reservoir Engineernarrow the potentail candidate wells quickly, efficiently and in anauditable transparent fashion. The Drilling Engineer can then startdetailed well planning.

The selection criteria used for the first stage of the process is saved sothat if the programme is run again for the same target the next usercan see which previous criteria were used.

The programme allows you to go back and continue the analysis aftereach stage. The results can be saved and edited as required. Thesystem is transparant and the decision-making steps are clear.

The program is designed to operate systematically so that everyengineer takes the same steps when selecting the most appropriatecandidate well.

Disadvantages

The initial time-consuming stage of the programme, remains theentering of data into the database. Most operators will find thatconsiderable time needs to be spent searching through well files infinding paper-based information. A futher issue is data quality. Even ifan operator has a computer database of data, verifying that storedinformation is correct is still a formidable task. This will become less ofan issue as more well information is stored electronically and the datais then used for further planning using a variety of tools. Well Analysisand Selection Process (WASP) is based on a database and as moreand more information is stored the program will slows down.

During the initial trial of the system, a number of errors in well filerecords were found and the system highlighted that in order for theprogram to function properly the information entered into the programwould need to be accurate.

Future Development

There are further developments planned for WASP. An Underbalancedcandidate selection module is currently being designed.

A cost module is also under development as an additional tool, whichwill allow a geologist to enter a reservoir target and in combination withreservoir simulation tools allow him to quickly identify if a well iseconomic as a sidetrack. A cost estimate of a planned sidetrack carriedout with coil or with a conventional rig in combination with hydrocarbonrecovery from a geological target allows rapid management decisionsto drill a sidetrack.

The tool is currently being re-developed in to a web based system willwhich will allow rig site data entry and multi user data entry. It will also

provide the ability to select sidetrack wells and systems in meetingswith partners by entering a number of different targets.

The Well Analysis and Selection Process has been successfullyapplied to Talismans Buchan Field, Kerr McGees Murchison, NinianNorth and Hutton field and Shell Expro UK Ltds NorthernBusiness Unit.

Each Operator incurred a considerable reduction in candidate selection

time and realised significant savings in engineering time. The processis transparant and can easily report why a well is the most suitablecandidate. A change to any of the criteria does not render previouswork unusable but a new target can rapidly be analysed for suitability.

Conclusions

Using a standard methodology for selecting sidetrack technology andthe associated candidate wells results in significant cost and timesavings in pre engineering time. It allows management decisions to bemade as informed decisions and it provides an auditable trial of why awell was selected or rejected as a suitable candidate.

With the current high demand on drilling engineers time, all managerswant to see engineers do what they are good at and that is well

engineering and not spending time in archives trying to find the latesttubing data in a candidate well. By allowing technical assistants toenter the well data and by allowing geologists to provide as manytargets as they can find, the drilling engineers can quickly select a bestoption from an operational and economical view point for a sidetrack.This in turn allows an operator to access the passed oil and recover itbefore depletion or other factors make this process impossible.

By using existing well data for planning purposes, the accuracy of thedata improves and this will allow faster management decisions inthe future.

The system has already been proven in selecting candidates from over200 in wells Brent and Cormorant field in the North Sea where theoptimum TTRD candidates are selected in a matter of days once thereservoir target has been selected.

List of Figures

Fig 1: Main Menu ScreenFig 2: Wells Database Casing/Liner ViewFig 3: Target Entry ScreenFig 4: Find Wells withing Distance ScreenFig 5: Operability MaskFig 6: Operability ResultsFig 7: Scoring AdministratorFig 8: Well Options Creation ScreenFig 9: CTD Well OptionFig 10: CTD Drillability MaskFig 11: Final Results Screen


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Fig 1: Main Menu Screen

Fig 2: Wells Database - Casing/Liner View

Fig 3: Target Entry Screen


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Fig 4: Find Wells within Distance

Fig 5. Operability Mask

Fig 6: Operability Results


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Fig 7: Scoring Administrator

Fig 8: Screen for Creation of Wellpath Options

Fig 9: CTD Wellpath Option


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Fig 10. CTD Drillability Mask

Fig 11. Final Results Screen

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